Current lighting devices often employ digital lighting technologies such as light-emitting diodes (LEDs) that generally feature longer operating lives, cheaper operating costs, and wider color ranges than those of legacy lighting devices such as incandescent lamps and fluorescent lamps. LEDs not only produce light using less energy than legacy lamps, but also feature directional light emission that allows for more effective delivery of light precisely on target. However, two design aspects of digital lighting solutions that are critical particularly for outdoor lamps are minimizing light waste and reducing glare.
Changing ambient light conditions (e.g., seasonal differences, time of day, subjects in motion) can cause lighting device emissions of a given color to be absorbed by the surrounding environment rather than reflected for perception by the user of the lighting device. Such light waste operates counter to the longevity, affordability, and efficiency of digital lighting devices. Advancements in generation of colored light and adaptation to ambient light conditions hold promise for combating light waste.
U.S. patent application Ser. No. 13/775,936 titled Adaptive Light System and Associated Methods discloses a lighting device that dynamically adapts to a changing ambient environment so that more of its produced light is reflected rather than absorbed, increasing efficiency. More specifically, the light adapter may accept a source signal defining a detected color, and may efficiently manipulate two color points generated by primary light sources along with a white color point generated by a high efficacy light source to produce the detected color. However, enhancing some detected colors under certain ambient lighting conditions may result in an increased perception of glare by the user of the lighting device. Glare is commonly categorized as either discomfort glare or disability glare. Disability glare is a scattering of light in the eye of a viewer which is perceived as a luminous veil over the scene, thereby reducing visibility. Discomfort glare is a sensation of annoyance or distraction that does not necessarily impair the visibility of objects. Discomfort glare may not be blinding, but nonetheless may have negative implications, particularly for driving performance and safety.
Discomfort glare is impacted by several factors. Light sources with higher luminous intensities may be perceived as more glaring. Similarly, perceptions of discomfort may increase as ambient lighting illuminance is reduced, and also as glare sources come closer to the line of sight of the viewer. Furthermore, research into spectral power distribution (SPD), which is a quantitative measure of the amount of energy emitted at different wavelengths, suggests that short wavelength light contributes more to the discomfort glare response than do most higher-wavelength lights.
Regarding SPD as a glare-producing factor, different lamps have different spectral characteristics that are often visible to humans (e.g., wavelengths in the range of about 380 to 760 nanometers (nm)). “Warm white” sources, such as incandescent bulbs, emit more strongly at the middle and longer (red) wavelengths. “Cool white” sources, including many LEDs, feature a spectral power distribution favoring short wavelengths (blue and violet). Although LEDs can be made in nearly every visible color, the most efficient formulations are rich in blue light because blue wavelengths activate phosphors which provide the other colors necessary for high quality white light.
Studies suggest that blue-rich white light causes more glare than longer wavelength lights at like illuminances, with later studies confirming a wavelength in the range of 420 nm to 480 nm to be most closely linked with discomfort glare. The same studies determined the least amount of discomfort was seen with a 577 nm stimulus. Generally, a light source with increased spectral output below 500 nm may increase the perception of glare, particularly for older people, and may be more likely to hinder vision than a conventional source of the same intensity. Various approaches to reducing discomfort glare by removing known contributing factors are known in the art.
U.S. Pat. No. 6,450,652 to Karpen discloses doping a motor vehicle windshield with Neodymium Oxide to filter the yellow portion of the spectrum from a driver's perception. Elimination of yellow light may lessen glare and improve contrast of objects during night driving when only artificial illumination is available. However, such a light filter not only fails to adapt to changing ambient light conditions, but also operates to hinder visibility of objects that reflect wavelengths in the fixed spectral region being filtered, both in daylight and at night.
European Patent No. 1,671,059 to Schottland et al. discloses incorporating dyes and design features into the lens for a lamp for the purpose of shifting the chromaticity of the light source. Using such a lens to manipulate an emitted beam may reduce discomfort glare and/or increase brightness to enhance visibility at night to the human eye. However, like the Karpen patent above, the fixed lens design is not equipped to adapt to changing ambient light conditions based on the unique spectral characteristics of various objects passing through the illumination range of the light source.
European Patent Application No. 2,292,464 by Tatara et al. discloses a vehicle headlight system configured to selectively illuminate a region in front of the vehicle with an adaptable illumination pattern. A target object in front of the vehicle is extracted from an image frame, and a light distribution pattern is selected that suppresses glare directed at the target object. However, manipulation of image patterns does nothing to enhance a target object for viewing based on the color of the object, nor to reduce glare produced by light reflected from the target object.
A need exists for a light adapter that may accept a source signal defining a detected color, and that may efficiently manipulate two or more color points generated by primary light sources along with a white color point generated by a high efficacy light source to produce the detected color. Additionally, a lighting device with the ability to adapt to a detected color would be able to dynamically increase its efficiency by allowing for reduced light absorption by the lighting device's environment, but without causing a discomfort glare response at the detected color. More specifically, a need exists for a lighting device with the ability to adapt to its environment so that more of its produced light is reflected rather than absorbed, and simultaneously to counteract discomfort glare contributed to by the produced light. Additionally, such a lighting device may need to adapt multiple times to account for changes in its environment.
This background information is provided to reveal information believed to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.